Network Working Group K. Murchison, Ed.

Network Working Group K. Murchison, Ed.
Request for Comments: 5536 Carnegie Mellon University
Obsoletes: 1036 C. Lindsey
Category: Standards Track University of Manchester
D. Kohn
Healing Thresholds
November 2009

Netnews Article Format

Abstract

This document specifies the syntax of Netnews articles in the context
of the Internet Message Format (RFC 5322) and Multipurpose Internet
Mail Extensions (MIME) (RFC 2045). This document obsoletes RFC 1036,
providing an updated specification to reflect current practice and
incorporating incremental changes specified in other documents.

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.

This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling

Murchison, et al. Standards Track [Page 1]

RFC 5536 Netnews Article Format November 2009

the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.

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RFC 5536 Netnews Article Format November 2009

Table of Contents

1. Introduction ....................................................4
1.1. Basic Concepts .............................................4
1.2. Scope ......................................................4
1.3. Requirements Notation ......................................4
1.4. Syntax Notation ............................................5
1.5. Definitions ................................................5
1.6. Structure of This Document .................................7
2. Format ..........................................................7
2.1. Base .......................................................7
2.2. Header Fields ..............................................8
2.3. MIME Conformance ...........................................9
3. News Header Fields ..............................................9
3.1. Mandatory Header Fields ...................................10
3.1.1. Date ...............................................11
3.1.2. From ...............................................11
3.1.3. Message-ID .........................................11
3.1.4. Newsgroups .........................................13
3.1.5. Path ...............................................14
3.1.6. Subject ............................................16
3.2. Optional Header Fields ....................................16
3.2.1. Approved ...........................................17
3.2.2. Archive ............................................17
3.2.3. Control ............................................17
3.2.4. Distribution .......................................18
3.2.5. Expires ............................................19
3.2.6. Followup-To ........................................19
3.2.7. Injection-Date .....................................20
3.2.8. Injection-Info .....................................20
3.2.9. Organization .......................................22
3.2.10. References ........................................22
3.2.11. Summary ...........................................23
3.2.12. Supersedes ........................................23
3.2.13. User-Agent ........................................23
3.2.14. Xref ..............................................24
3.3. Obsolete Header Fields ....................................25
3.3.1. Lines ..............................................25
4. Internationalization Considerations ............................25
5. Security Considerations ........................................25
6. IANA Considerations ............................................26
7. References .....................................................31
7.1. Normative References ......................................31
7.2. Informative References ....................................32
Appendix A. Acknowledgments ......................................34
Appendix B. Differences from RFC 1036 and Its Derivatives ........34
Appendix C. Differences from RFC 5322 ............................35

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RFC 5536 Netnews Article Format November 2009

1. Introduction

1.1. Basic Concepts

"Netnews" is a set of protocols for generating, storing, and
retrieving news "articles" (whose format is a subset of that for
Email messages), and for exchanging them amongst a readership that is
potentially widely distributed. It is organized around "newsgroups",
with the expectation that each reader will be able to see all
articles posted to each newsgroup in which he participates. These
protocols most commonly use a flooding algorithm, which propagates
copies throughout a network of participating servers. Typically,
only one copy is stored per server, and each server makes it
available on demand to readers who are able to access that server.

1.2. Scope

This document specifies the syntax of Netnews articles in the context
of the Internet Message Format [RFC5322] and Multipurpose Internet
Mail Extensions (MIME) [RFC2045]. This document obsoletes [RFC1036],
updating the syntax of Netnews articles to reflect current practice
and incorporating changes and clarifications specified in other
documents such as [Son-of-1036].

This is the first in a set of documents that obsolete [RFC1036].
This document focuses on the syntax and semantics of Netnews
articles. [RFC5537] is also a Standards Track document and describes
the protocol issues of Netnews articles, independent of transport
protocols such as the Network News Transfer Protocol (NNTP)
[RFC3977]. [USEAGE], "Usenet Best Practice", describes
implementation recommendations to improve interoperability and
usability.

This specification is intended as a definition of what article
content format is to be passed between systems. Although many news
systems locally store articles in this format (which eliminates the
need for translation between formats), local storage is outside of
the scope of this standard.

1.3. Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

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RFC 5536 Netnews Article Format November 2009

1.4. Syntax Notation

Header fields defined in this specification use the Augmented Backus-
Naur Form (ABNF) notation (including the Core Rules) specified in
[RFC5234] as well as many constructs defined in [RFC5322], [RFC2045]
as updated by [RFC2231], and [RFC3986]. Specifically:

token = <see RFC 2045 Section 5.1>
value = <see RFC 2045 Section 5.1>
parameter = <see RFC 2231 Section 7>
attribute = <see RFC 2231 Section 7>

FWS = <see RFC 5322 Section 3.2.2>
comment = <see RFC 5322 Section 3.2.2>
CFWS = <see RFC 5322 Section 3.2.2>
atext = <see RFC 5322 Section 3.2.3>
dot-atom-text = <see RFC 5322 Section 3.2.3>
phrase = <see RFC 5322 Section 3.2.5>
date-time = <see RFC 5322 Section 3.3>
mailbox = <see RFC 5322 Section 3.4>
mailbox-list = <see RFC 5322 Section 3.4>
address-list = <see RFC 5322 Section 3.4>
body = <see RFC 5322 Section 3.5>
fields = <see RFC 5322 Section 3.6>

IPv6address = <see RFC 3986 Section 3.2.2>
IPv4address = <see RFC 3986 Section 3.2.2>

ALPHA = <see RFC 5234 Appendix B.1>
CRLF = <see RFC 5234 Appendix B.1>
DIGIT = <see RFC 5234 Appendix B.1>
DQUOTE = <see RFC 5234 Appendix B.1>
SP = <see RFC 5234 Appendix B.1>
VCHAR = <see RFC 5234 Appendix B.1>

Additionally, Section 3.1.3 specifies a stricter definition of
<msg-id> than the syntax in Section 3.6.4 of [RFC5322].

1.5. Definitions

An "article" is the unit of Netnews, analogous to an [RFC5322]
"message". A "proto-article" is one that has not yet been injected
into the news system. In contrast to an article, a proto-article may
lack some mandatory header fields.

A "message identifier" (Section 3.1.3) is a unique identifier for an
article, usually supplied by the user agent that posted it or,
failing that, by the "news server". It distinguishes the article

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RFC 5536 Netnews Article Format November 2009

from every other article ever posted anywhere. Articles with the
same message identifier are treated as if they are the same article
regardless of any differences in the body or header fields.

A "newsgroup" is a forum having a name and that is intended for
articles on a specific topic. An article is "posted to" a single
newsgroup or several newsgroups. When an article is posted to more
than one newsgroup, it is said to be "crossposted"; note that this
differs from posting the same text as part of each of several
articles, one per newsgroup.

A newsgroup may be "moderated", in which case submissions are not
posted directly, but mailed to a "moderator" for consideration and
possible posting. Moderators are typically human but may be
implemented partially or entirely in software.

A "poster" is the person or software that composes and submits a
potentially compliant article to a user agent.

A "reader" is the person or software reading Netnews articles.

A "followup" is an article containing a response to the contents of
an earlier article, its "precursor". Every followup includes a
"References" header field identifying that precursor (but note that
non-followup articles may also use a References header field).

A "control message" is an article that is marked as containing
control information; a news server receiving such an article may
(subject to the policies observed at that site) take actions beyond
just filing and passing on the article.

A news server is software that may accept articles from a user agent,
and/or make articles available to user agents, and/or exchange
articles with other news servers.

A "user agent" is software that may help posters submit proto-
articles to a news server, and/or fetch articles from a news server
and present them to a reader, and/or assist the reader in creating
articles and followups.

The generic term "agent" is used when describing requirements that
apply to both user agents and news servers.

An agent is said to "generate" a construct if it did not exist before
the agent created it. Examples are when a user agent creates a
message from text and addressing information supplied by a user, or
when a news server creates an "Injection-Info" header field for a
newly posted message.

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RFC 5536 Netnews Article Format November 2009

An agent is said to "accept" a construct if some other entity
generates it and passes it to the agent in question, and the agent
processes it without treating it as a format or protocol error.

1.6. Structure of This Document

This document uses a cite-by-reference methodology, rather than
repeating the contents of other standards, which could otherwise
result in subtle differences and interoperability challenges.
Although this document is as a result rather short, it requires
complete understanding and implementation of the normative references
to be compliant.

Section 2 defines the format of Netnews articles. Section 3 details
the header fields necessary to make an article suitable for the
Netnews environment.

2. Format

2.1. Base

An article is said to be conformant to this specification if it
conforms to the format specified in Section 3 of [RFC5322] and to the
additional requirements of this specification.

An article that uses the obsolete syntax specified in Section 4 of
[RFC5322] is NOT conformant to this specification, except for the
following two cases:

o Articles are conformant if they use the <obs-phrase> construct
(use of a phrase like "John Q. Public" without the use of quotes,
see Section 4.1 of [RFC5322]), but agents MUST NOT generate
productions of such syntax.

o Articles are conformant if they use the "GMT" <zone>, as specified
in Section 3.1.1.

This document, and specifications that build upon it, specify how to
handle conformant articles. Handling of non-conformant articles is
outside the scope of this specification.

Agents conforming to this specification MUST generate only conformant
articles.

The text below uses ABNF to specify restrictions on the syntax
specified in [RFC5322]; this grammar is intended to be more
restrictive than the [RFC5322] grammar. Articles must conform to the

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RFC 5536 Netnews Article Format November 2009

ABNF specified in [RFC5322] and also to the restrictions specified
here, both those that are expressed as text and those that are
expressed as ABNF.

NOTE: Other specifications use the term "header" as a synonym for
what [RFC5322] calls "header field". This document follows the
terminology in Section 2 of [RFC5322] in using the terms "line",
"header field", "header field name", "header field body", and
"folding", based on a belief that consistent terminology among
specifications that depend on each other makes the specifications
easier to use in the long run.

2.2. Header Fields

All header fields in a Netnews article are compliant with [RFC5322];
this specification, however, is less permissive in what can be
generated and accepted by agents. The syntax allowed for Netnews
article headers is a strict subset of the Internet Message Format
headers, making all headers compliant with this specification
inherently compliant with [RFC5322]. Note however that the converse
is not guaranteed to be true in all cases.

General rules that apply to all header fields (even those documented
in [RFC5322] and [RFC2045]) are listed below, and those that apply to
specific header fields are described in the relevant sections of this
document.

o All agents MUST generate header fields so that at least one space
immediately follows the ':' separating the header field name and
the header field body (for compatibility with deployed software,
including NNTP [RFC3977] servers). News agents MAY accept header
fields that do not contain the required space.

o Every line of a header field body (including the first and any
that are subsequently folded) MUST contain at least one non-
whitespace character.

NOTE: This means that no header field body defined by or
referenced by this document can be empty. As a result, rather
than using the <unstructured> syntax from Section 3.2.5 of
[RFC5322], this document uses a stricter definition:

unstructured = *WSP VCHAR *( [FWS] VCHAR ) *WSP

NOTE: The [RFC5322] specification sometimes uses [FWS] at the
beginning or end of ABNF describing header field content. This
specification uses *WSP in such cases, also in cases where this
specification redefines constructs from [RFC5322]. This is

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RFC 5536 Netnews Article Format November 2009

done for consistency with the restriction described here, but
the restriction applies to all header fields, not just those
where ABNF is defined in this document.

o Compliant software MUST NOT generate (but MAY accept) header field
lines of more than 998 octets. This is the only limit on the
length of a header field line prescribed by this standard.
However, specific rules to the contrary may apply in particular
cases (for example, according to [RFC2047], lines of a header
field containing encoded words are limited to 76 octets).
[USEAGE] includes suggested limits for convenience of display by
user agents.

NOTE: As stated in [RFC5322], there is NO restriction on the
number of lines into which a header field may be split, and
hence there is NO restriction on the total length of a header
field (in particular it may, by suitable folding, be made to
exceed the 998-octet restriction pertaining to a single header
field line).

o The character set for header fields is US-ASCII. Where the use of
non-ASCII characters is required, they MUST be encoded using the
MIME mechanisms defined in [RFC2047] and [RFC2231].

2.3. MIME Conformance

User agents MUST meet the definition of MIME conformance in [RFC2049]
and MUST also support [RFC2231]. This level of MIME conformance
provides support for internationalization and multimedia in message
bodies [RFC2045], [RFC2046], and [RFC2231], and support for
internationalization of header fields [RFC2047] and [RFC2231]. Note
that [Errata] currently exist for [RFC2045], [RFC2046], [RFC2047] and
[RFC2231].

For the purposes of Section 5 of [RFC2047], all header fields defined
in Section 3 of this standard are to be considered as "extension
message header fields", permitting the use of [RFC2047] encodings
within any <unstructured> header field, or within any <comment> or
<phrase> permitted within any structured header field.

User agents MAY accept and generate other MIME extension header
fields, and in particular SHOULD accept Content-Disposition [RFC2183]
and Content-Language [RFC3282].

3. News Header Fields

The following news header fields extend those defined in Section 3.6
of [RFC5322]:

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RFC 5536 Netnews Article Format November 2009

fields =/ *( approved /
archive /
control /
distribution /
expires /
followup-to /
injection-date /
injection-info /
lines /
newsgroups /
organization /
path /
summary /
supersedes /
user-agent /
xref )

Each of these header fields MUST NOT occur more than once in a news
article.

The following header fields defined in this document do not allow
<comment>s (i.e., they use FWS rather than CFWS).

Control
Distribution
Followup-To
Lines
Newsgroups
Path
Supersedes
Xref

This also applies to the following header field defined in [RFC5322]:

Message-ID

Most of these header fields are mainly of interest to news servers,
and news servers often need to process these fields very rapidly.
Thus, some header fields prohibit <comment>s.

3.1. Mandatory Header Fields

Each Netnews article conformant with this specification MUST have
exactly one of each of the following header fields: Date, From,
Message-ID, Newsgroups, Path, and Subject.

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3.1.1. Date

The Date header field is the same as that specified in Sections 3.3
and 3.6.1 of [RFC5322], with the added restrictions detailed above in
Section 2.2. However, the use of "GMT" as a time zone (part of
<obs-zone>), although deprecated, is widespread in Netnews articles
today. Therefore, agents MUST accept <date-time> constructs that use
the "GMT" zone.

orig-date = "Date:" SP date-time CRLF

NOTE: This specification does not change [RFC5322], which says
that agents MUST NOT generate <date-time> constructs that include
any zone names defined by <obs-zone>.

Software that accepts dates with unknown timezones SHOULD treat such
timezones as equivalent to "-0000" when comparing dates, as specified
in Section 4.3 of [RFC5322].

Also note that these requirements apply wherever <date-time> is used,
including Injection-Date and Expires (Sections 3.2.7 and 3.2.5,
respectively).

3.1.2. From

The From header field is the same as that specified in Section 3.6.2
of [RFC5322], with the added restrictions detailed above in
Section 2.2.

from = "From:" SP mailbox-list CRLF

3.1.3. Message-ID

The Message-ID header field contains a unique message identifier.
Netnews is more dependent on message identifier uniqueness and fast
comparison than Email is, and some news software and standards
[RFC3977] might have trouble with the full range of possible
<msg-id>s permitted by [RFC5322]. This section therefore restricts
the syntax of <msg-id> as compared to Section 3.6.4 of [RFC5322].
The global uniqueness requirement for <msg-id> in [RFC5322] is to be
understood as applying across all protocols using such message
identifiers, and across both Email and Netnews in particular.

message-id = "Message-ID:" SP *WSP msg-id *WSP CRLF

msg-id = "<" msg-id-core ">"
; maximum length is 250 octets

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RFC 5536 Netnews Article Format November 2009

msg-id-core = id-left "@" id-right

id-left = dot-atom-text

id-right = dot-atom-text / no-fold-literal

no-fold-literal = "[" *mdtext "]"

mdtext = %d33-61 / ; The rest of the US-ASCII
%d63-90 / ; characters not including
%d94-126 ; ">", "[", "]", or "\"

The <msg-id> MUST NOT be more than 250 octets in length.

NOTE: The length restriction ensures that systems that accept
message identifiers as a parameter when referencing an article
(e.g., [RFC3977]) can rely on a bounded length.

Observe that <msg-id> includes the < and >.

Observe also that in contrast to the corresponding header field in
[RFC5322]:

o The syntax does not allow comments within the Message-ID header
field.

o There is no possibility for ">" or WSP to occur inside a <msg-id>.

o Even though commonly derived from <domain>s, <id-rights>s are
case-sensitive (and thus, once created, are not to be altered
during subsequent transmission or copying)

This is to simplify processing by news servers and to ensure
interoperability with existing implementations and compliance with
[RFC3977]. A simple comparison of octets will always suffice to
determine the identity of two <msg-id>s.

Also note that this updated ABNF applies wherever <msg-id> is used,
including the References header field discussed in Section 3.2.10 and
the Supersedes header field discussed in Section 3.2.12.

Some software will try to match the <id-right> of a <msg-id> in a
case-insensitive fashion; some will match it in a case-sensitive
fashion. Implementations MUST NOT generate a Message-ID where the
only difference from another Message-ID is the case of characters in
the <id-right> part.

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RFC 5536 Netnews Article Format November 2009

When generating a <msg-id>, implementations SHOULD use a domain name
as the <id-right>.

NOTE: Section 3.6.4 of [RFC5322] recommends that the <id-right>
should be a domain name or a domain literal. Domain literals are
troublesome since many IP addresses are not globally unique;
domain names are more likely to generate unique Message-IDs.

3.1.4. Newsgroups

The Newsgroups header field specifies the newsgroup(s) to which the
article is posted.

newsgroups = "Newsgroups:" SP newsgroup-list CRLF

newsgroup-list = *WSP newsgroup-name
*( [FWS] "," [FWS] newsgroup-name ) *WSP

newsgroup-name = component *( "." component )

component = 1*component-char

component-char = ALPHA / DIGIT / "+" / "-" / "_"

Not all servers support optional FWS in the list of newsgroups. In
particular, folding the Newsgroups header field over several lines
has been shown to harm propagation significantly. Optional FWS in
the <newsgroup-list> SHOULD NOT be generated, but MUST be accepted.

A <component> SHOULD NOT consist solely of digits and SHOULD NOT
contain uppercase letters. Such <component>s MAY be used only to
refer to existing groups that do not conform to this naming scheme,
but MUST NOT be used otherwise.

NOTE: All-digit <component>s conflict with one widely used storage
scheme for articles. Mixed-case groups cause confusion between
systems with case-sensitive matching and systems with case-
insensitive matching of <newsgroup-name>s.

<component>s beginning with underline ("_") are reserved for use by
future versions of this standard and SHOULD NOT be generated by user
agents (whether in header fields or in newgroup control messages as
defined by [RFC5537]). However, such names MUST be accepted by news
servers.

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<component>s beginning with "+" and "-" are reserved for private use
and SHOULD NOT be generated by user agents (whether in header fields
or in newgroup control messages [RFC5537]) without a private prior
agreement to do so. However, such names MUST be accepted by news
servers.

The following <newsgroup-name>s are reserved and MUST NOT be used as
the name of a newsgroup:

o Groups whose first (or only) <component> is "example"

o The group "poster"

The following <newsgroup-name>s have been used for specific purposes
in various implementations and protocols and therefore MUST NOT be
used for the names of normal newsgroups. They MAY be used for their
specific purpose or by local agreement.

o Groups whose first (or only) component is "to"

o Groups whose first (or only) component is "control"

o Groups that contain (or consist only of) the component "all"

o Groups that contain (or consist only of) the component "ctl"

o The group "junk"

NOTE: "example.*" is reserved for examples in this and other
standards; "poster" has a special meaning in the Followup-To
header field; "to.*" is reserved for certain point-to-point
communications in conjunction with the "ihave" control message as
defined in [RFC5537]; "control.*" and "junk" have special meanings
in some news servers; "all" is used as a wildcard in some
implementations; and "ctl" was formerly used to indicate a
<control-command> within the Newsgroups header field.

3.1.5. Path

The Path header field indicates the route taken by an article since
its injection into the Netnews system. Each agent that processes an
article is required to prepend at least one <path-identity> to this
header field body. This is primarily so that news servers are able
to avoid sending articles to sites already known to have them, in
particular the site they came from. Additionally, it permits
gathering statistics and tracing the route articles take in moving
over the network.

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RFC 5536 Netnews Article Format November 2009

path = "Path:" SP *WSP path-list tail-entry *WSP CRLF

path-list = *( path-identity [FWS] [path-diagnostic] "!" )

path-diagnostic = diag-match / diag-other / diag-deprecated

diag-match = "!" ; another "!"

diag-other = "!." diag-keyword [ "." diag-identity ] [FWS]

diag-deprecated = "!" IPv4address [FWS]

diag-keyword = 1*ALPHA ; see [RFC5537]

diag-identity = path-identity / IPv4address / IPv6address

tail-entry = path-nodot
; may be the string "not-for-mail"

path-identity = ( 1*( label "." ) toplabel ) / path-nodot

path-nodot = 1*( alphanum / "-" / "_" ) ; legacy names

label = alphanum [ *( alphanum / "-" ) alphanum ]

toplabel = ( [ label *( "-" ) ] ALPHA *( "-" ) label ) /
( label *( "-" ) ALPHA [ *( "-" ) label ] ) /
( label 1*( "-" ) label )

alphanum = ALPHA / DIGIT ; compare [RFC3696]

A <path-identity> is a name identifying a site. It takes the form of
a domain name having two or more components separated by dots, or a
single name with no dots (<path-nodot>).

Each <path-identity> in the <path-list> (which does not include the
<tail-entry>) indicates, from right to left, the successive agents
through which the article has passed. The use of the <diag-match>,
which appears as "!!", indicates that the agent to its left verified
the identity of the agent to its right before accepting the article
(whereas the <path-delimiter> "!" implies no such claim).

NOTE: Historically, the <tail-entry> indicated the name of the
sender. If not used for this purpose, the string "not-for-mail"
is often used instead (since at one time the whole path could be
used as a mail address for the sender).

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RFC 5536 Netnews Article Format November 2009

NOTE: Although case-insensitive, it is intended that the
<diag-keyword>s should be in uppercase, to distinguish them from
the <path-identity>s, which are traditionally in lowercase.

A <path-diagnostic> is an item inserted into the Path header field
for purposes other than to indicate the name of a site. The use of
these is described in [RFC5537].

NOTE: One usage of a <path-diagnostic> is to record an IP address.
The fact that <IPv6address>es are allowed means that the colon (:)
is permitted; note that this may cause interoperability problems
at older sites that regard ":" as a <path-delimiter> and have
neighbors whose names have 4 or fewer characters, and where all
the characters are valid HEX digits.

NOTE: Although <IPv4address>es have occasionally been used in the
past (usually with a diagnostic intent), their continued use is
deprecated (though it is still acceptable in the form of the
<diag-deprecated>).

3.1.6. Subject

The Subject header field is the same as that specified in Section
3.6.5 of [RFC5322], with the added restrictions detailed above in
Section 2.2. Further discussion of the content of the Subject header
field appears in [RFC5537] and [USEAGE].

subject = "Subject:" SP unstructured CRLF

3.2. Optional Header Fields

None of the header fields appearing in this section are required to
appear in every article, but some of them may be required in certain
types of articles. Further discussion of these requirements appears
in [RFC5537] and [USEAGE].

The header fields Comments, Keywords, Reply-To, and Sender are used
in Netnews articles in the same circumstances and with the same
meanings as those specified in [RFC5322], with the added restrictions
detailed above in Section 2.2. Multiple occurrences of the Keywords
header field are not permitted.

comments = "Comments:" SP unstructured CRLF

keywords = "Keywords:" SP phrase *("," phrase) CRLF

Murchison, et al. Standards Track [Page 16]

RFC 5536 Netnews Article Format November 2009

reply-to = "Reply-To:" SP address-list CRLF

sender = "Sender:" SP mailbox CRLF

The MIME header fields MIME-Version, Content-Type, Content-Transfer-
Encoding, Content-Disposition, and Content-Language are used in
Netnews articles in the same circumstances and with the same meanings
as those specified in [RFC2045], [RFC2183], and [RFC3282], with the
added restrictions detailed above in Section 2.2.

All remaining news header fields are described below.

3.2.1. Approved

The Approved header field indicates the mailing addresses (and
possibly the full names) of the persons or entities approving the
article for posting. Its principal uses are in moderated articles
and in group control messages; see [RFC5537].

approved = "Approved:" SP mailbox-list CRLF

3.2.2. Archive

The Archive header field provides an indication of the poster's
intent regarding preservation of the article in publicly accessible
long-term or permanent storage.

archive = "Archive:" SP [CFWS] ("no" / "yes")
*( [CFWS] ";" [CFWS] archive-param ) [CFWS] CRLF

archive-param = parameter

The presence of an Archive header field in an article with a field
body of "no" indicates that the poster does not permit redistribution
from publicly accessible long-term or permanent archives. A field
body of "yes" indicates that the poster permits such redistribution.

No <parameter>s are currently defined; if present, they can be
ignored. Further discussion of the use of the Archive header field
appears in [USEAGE].

3.2.3. Control

The Control header field marks the article as a control message and
specifies the desired actions (in addition to the usual actions of
storing and/or relaying the article).

Murchison, et al. Standards Track [Page 17]

RFC 5536 Netnews Article Format November 2009

control = "Control:" SP *WSP control-command *WSP CRLF

control-command = verb *( 1*WSP argument )

verb = token

argument = 1*( %x21-7E )

The verb indicates what action should be taken, and the argument(s)
(if any) supply details. In some cases, the <body> (as defined in
[RFC5322]) of the article may also contain details. The legal verbs
and respective arguments are discussed in the companion document,
[RFC5537].

An article with a Control header field MUST NOT also have a
Supersedes header field.

3.2.4. Distribution

The Distribution header field specifies geographic or organizational
limits on an article's propagation.

distribution = "Distribution:" SP dist-list CRLF

dist-list = *WSP dist-name
*( [FWS] "," [FWS] dist-name ) *WSP

dist-name = ALPHA / DIGIT
*( ALPHA / DIGIT / "+" / "-" / "_" )

The <dist-name>s "world" and "local" are reserved. "world" indicates
unlimited distribution and SHOULD NOT be used explicitly, since it is
the default when the Distribution header field is absent entirely.
"local" is reserved for indicating distribution only to the local
site, as defined by local software configuration.

"All" MUST NOT be used as a <dist-name>. <dist-name>s SHOULD contain
at least three characters, except when they are two-letter country
codes drawn from [ISO3166-1]. <dist-name>s are case-insensitive
(i.e., "US", "Us", "uS", and "us" all specify the same distribution).

Optional FWS in the <dist-list> SHOULD NOT be generated, but MUST be
accepted.

Murchison, et al. Standards Track [Page 18]

RFC 5536 Netnews Article Format November 2009

3.2.5. Expires

The Expires header field specifies a date and time when the poster
deems the article to be no longer relevant and could usefully be
removed ("expired").

NOTE: This header field is useful when the poster desires an
unusually long or an unusually short expiry time.

expires = "Expires:" SP date-time CRLF

See the remarks under Section 3.1.1 regarding the syntax of
<date-time> and the requirements and recommendations to which it is
subject.

NOTE: The Expires header field is also sometimes used in Email
with a similar meaning; see [RFC2156].

3.2.6. Followup-To

The Followup-To header field specifies to which newsgroup(s) the
poster has requested that followups are to be posted. The
Followup-To header field SHOULD NOT appear in a message, unless its
content is different from the content of the Newsgroups header field.

followup-to = "Followup-To:" SP ( newsgroup-list / poster-text )
CRLF

poster-text = *WSP %d112.111.115.116.101.114 *WSP
; "poster" in lowercase

The syntax is the same as that of the Newsgroups (Section 3.1.4)
header field, with the exception that the keyword "poster" requests
that followups should be emailed directly to the article's poster
(using the addresses contained in the Reply-To header field if one
exists, otherwise using the addresses contained in the From header
field) rather than posted to any newsgroups. Agents MUST generate
the keyword "poster" in lowercase, but MAY choose to recognize case-
insensitive forms such as "Poster".

As in the Newsgroups (Section 3.1.4) header field, optional FWS in
the <newsgroup-list> SHOULD NOT be generated, but MUST be accepted.

Murchison, et al. Standards Track [Page 19]

RFC 5536 Netnews Article Format November 2009

3.2.7. Injection-Date

The Injection-Date header field contains the date and time that the
article was injected into the network. Its purpose is to enable news
servers, when checking for "stale" articles, to use a <date-time>
that was added by a news server at injection time rather than one
added by the user agent at message composition time.

This header field MUST be inserted whenever an article is injected.
However, software that predates this standard does not use this
header, and therefore agents MUST accept articles without the
Injection-Date header field.

injection-date = "Injection-Date:" SP date-time CRLF

See the remarks under Section 3.1.1 regarding the syntax of
<date-time> and the requirements and recommendations to which it is
subject.

NOTE: Since clocks on various agents are not necessarily
synchronized, the <date-time> in this header field might not be a
later value than that in the Date header field. Agents MUST NOT
alter a pre-existing Date header field when adding an Injection-
Date header field.

This header field is intended to replace the currently used but
undocumented "NNTP-Posting-Date" header field, whose use is now
deprecated.

3.2.8. Injection-Info

The Injection-Info header field contains information provided by the
injecting news server as to how an article entered the Netnews
system; it assists in tracing the article's true origin. It can also
specify one or more addresses where complaints concerning the poster
of the article may be sent.

injection-info = "Injection-Info:" SP [CFWS] path-identity
[CFWS] *( ";" [CFWS] parameter ) [CFWS] CRLF

NOTE: The syntax of <parameter> (Section 5.1 of [RFC2045], as
amended by [RFC2231]), taken in conjunction with the folding rules
of [RFC0822] (note: not [RFC2822] or [RFC5322]), effectively
allows [CFWS] to occur on either side of the "=" inside a
<parameter>.

Murchison, et al. Standards Track [Page 20]

RFC 5536 Netnews Article Format November 2009

The following table gives the <attribute> and the format of the
<value> for each <parameter> defined for use with this header field.
At most, one occurrence of each such <parameter> is allowed.

<attribute> format of <value>
-------------------- -----------------
"posting-host" a <host-value>
"posting-account" any <value>
"logging-data" any <value>
"mail-complaints-to" an <address-list>

where

host-value = dot-atom-text / IPv4address / IPv6address /
(dot-atom-text ":" ( IPv4address / IPv6address ))

NOTE: Since any such <host-value> or <address-list> also has to be
a syntactically correct <value>, it will usually be necessary to
encapsulate it as a <quoted-string>, for example:

posting-host = "posting.example.com:192.0.2.1"

Other <attribute>s SHOULD NOT be used unless defined in extensions to
this standard. If non-standards-based <attribute>s are used, they
MUST begin with an "x-".

Although comments and folding of whitespace are permitted throughout
the Injection-Info header field, folding SHOULD NOT be used within
any <parameter>. Folding SHOULD only occur before or after the ";"
separating <parameter>s, and comments SHOULD only be used following
the last <parameter>.

NOTE: Some of this information has previously been sent in non-
standardized header fields such as NNTP-Posting-Host, X-Trace,
X-Complaints-To, and others. Once a news server generates an
Injection-Info header field, it should have no need to send these
non-standard header fields.

The "posting-host" <parameter> specifies the Fully Qualified Domain
Name (FQDN) and/or IP address (IPv4address or IPv6address) of the
host from which the news server received the article.

NOTE: If the "posting-host" <parameter> fails to deterministically
identify the host (e.g., dynamic IP address allocation), the
"posting-account" or "logging-data" <parameter> may provide
additional information about the true origin of the article.

Murchison, et al. Standards Track [Page 21]

RFC 5536 Netnews Article Format November 2009

The "posting-account" <parameter> identifies the source from which
that news server received the article, in a notation that can be
interpreted by the news server administrator. This notation can
include any information the administrator deems pertinent. In order
to limit the exposure of personal data, it SHOULD be given in a form
that cannot be interpreted by other sites. However, to make it
useful for rate limiting and abuse detection, two messages posted
from the same source SHOULD have the same value of "posting-account",
and two messages from different sources SHOULD have differing values
of "posting-account". The exact definition of "source" is left to
the discretion of the news server administrator.

The "logging-data" <parameter> contains information (typically a
session number or other non-persistent means of identifying a posting
account) that will enable the true origin of the article to be
determined by reference to logging information kept by the news
server.

The "mail-complaints-to" <parameter> specifies one or more mailboxes
for sending complaints concerning the behavior of the poster of the
article.

It is a matter of local policy which of the above <parameter>s to
include. Some pieces of information have privacy implications; this
is discussed in [USEAGE].

3.2.9. Organization

The Organization header field is a short phrase identifying the
poster's organization.

organization = "Organization:" SP unstructured CRLF

NOTE: There is no "s" in Organization.

3.2.10. References

The References header field is the same as that specified in Section
3.6.4 of [RFC5322], with the added restrictions detailed above in
Section 2.2 and those listed below:

o The updated <msg-id> construct defined in Section 3.1.3 MUST be
used.

o Message identifiers MUST be separated with CFWS.

Murchison, et al. Standards Track [Page 22]

RFC 5536 Netnews Article Format November 2009

o Comments in CFWS between message identifiers can cause
interoperability problems, so comments SHOULD NOT be generated but
MUST be accepted.

references = "References:" SP [CFWS] msg-id *(CFWS msg-id)
[CFWS] CRLF

3.2.11. Summary

The Summary header field is a short phrase summarizing the article's
content.

summary = "Summary:" SP unstructured CRLF

3.2.12. Supersedes

The Supersedes header field contains a message identifier specifying
an article to be superseded upon the arrival of this one. An article
containing a Supersedes header field is equivalent to a "cancel"
[RFC5537] control message for the specified article, followed
immediately by the new article without the Supersedes header field.

supersedes = "Supersedes:" SP *WSP msg-id *WSP CRLF

NOTE: There is no "c" in Supersedes.

NOTE: The Supersedes header field defined here has no connection
with the Supersedes header field that sometimes appears in Email
messages converted from X.400 according to [RFC2156]; in
particular, the syntax here permits only one <msg-id> in contrast
to the multiple <msg-id>s in that Email version.

3.2.13. User-Agent

The User-Agent header field contains information about the user agent
(typically a newsreader) generating the article, for statistical
purposes and tracing of standards violations to specific software in
need of correction. It is intended that this header field be
suitable for use in Email.

user-agent = "User-Agent:" SP 1*product [CFWS] CRLF

product = [CFWS] token [ [CFWS] "/" product-version ]

product-version = [CFWS] token

Murchison, et al. Standards Track [Page 23]

RFC 5536 Netnews Article Format November 2009

This header field MAY contain multiple <product> tokens identifying
the user agent and any subproducts that form a significant part of
it, listed in order of their significance for identifying the
application.

NOTE: Some of this information has previously been sent in non-
standardized header fields such as X-Newsreader, X-Mailer,
X-Posting-Agent, X-Http-User-Agent, and others. Once a user agent
generates a User-Agent header field, it should have no need to
send these non-standard header fields.

NOTE: [RFC2616] describes a similar facility for the HTTP
protocol. The Netnews article format differs in that "{" and "}"
are allowed in tokens (<product> and <product-version>) and
comments are permitted wherever white space is allowed.

3.2.14. Xref

The Xref header field indicates where an article was filed by the
last news server to process it. User agents often use the
information in the Xref header field to avoid multiple processing of
crossposted articles.

xref = "Xref:" SP *WSP server-name
1*( FWS location ) *WSP CRLF

server-name = path-identity

location = newsgroup-name ":" article-locator

article-locator = 1*( %x21-27 / %x29-3A / %x3C-7E )
; US-ASCII printable characters
; except '(' and ';'

The <server-name> is included so that software can determine which
news server generated the header field. The locations specify where
the article is filed -- i.e., under which newsgroups (which may
differ from those in the Newsgroups header field), and where under
those newsgroups. The exact form of an <article-locator> is
implementation-specific.

NOTE: The traditional form of an <article-locator> (as required by
[RFC3977]) is a decimal number, with articles in each newsgroup
numbered consecutively starting from 1.

Murchison, et al. Standards Track [Page 24]

RFC 5536 Netnews Article Format November 2009

3.3. Obsolete Header Fields

The header fields Date-Received, Posting-Version, and Relay-Version
defined in [RFC0850], as well as Also-Control, Article-Names,
Article-Updates, and See-Also defined in [Son-of-1036] are declared
obsolete. See the cited specification documents for further
information on their original use.

These header fields MUST NOT be generated and SHOULD be ignored.

3.3.1. Lines

The Lines header field indicates the number of lines in the <body>
(as defined in [RFC5322]) of the article.

lines = "Lines:" SP *WSP 1*DIGIT *WSP CRLF

The line count is the number of CRLF separators in the <body>.

Historically, this header field was used by the NNTP [RFC3977]
overview facility, but its use for this purpose is now deprecated.
As a result, this header field is to be regarded as obsolescent, and
it is likely to be removed entirely in a future version of this
standard. All agents SHOULD ignore it and SHOULD NOT generate it.

4. Internationalization Considerations

Internationalization of Netnews article header fields and bodies is
provided using the MIME mechanisms discussed in Section 2.3. Note
that the generation of internationalized <newsgroup-name>s for use in
header fields is not addressed in this document.

5. Security Considerations

The Netnews article format specified in this document does not
provide any security services, such as confidentiality,
authentication of sender, or non-repudiation. Instead, such services
need to be layered above, using such protocols as S/MIME [RFC3851] or
PGP/MIME (Pretty Good Privacy / MIME) [RFC3156], or below, using
secure versions of news transport protocols. Additionally, several
currently non-standardized protocols such as [PGPVERIFY] may be
standardized in the near future.

Message identifiers (Section 3.1.3) in Netnews articles are required
to be unique; articles may be refused (in server-to-server transfer)
if the identifier has already been seen. If a malicious agent can
predict the identifier of an article, it can preempt the article by
posting its own article (possibly to a quite different group) with

Murchison, et al. Standards Track [Page 25]

RFC 5536 Netnews Article Format November 2009

the same message identifier, thereby preventing the target article
from propagating. Therefore, agents that generate message
identifiers for Netnews articles SHOULD ensure that they are
unpredictable.

MIME security considerations are discussed in [RFC2046]. Note that
the full range of encodings allowed for parameters in [RFC2046] and
[RFC2231] permits constructs that simple parsers may fail to parse
correctly; examples of hard-to-parse constructs are:

Content-Type: multipart/mixed
(; boundary=foo ; xyz=");bOuNdArY*=''next%20part(")

Content-Type: multipart/digest;
boundary (not=me) = ("yes ;-) simple (foo;bar") ; x-foo = xyzzy

Such deficiencies in parsing may be used as part of an attack.

Further security considerations are discussed in [RFC5537].

6. IANA Considerations

IANA has registered the following header fields in the Permanent
Message Header Field Repository, in accordance with the procedures
set out in [RFC3864].

Header field name: Also-Control
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [Son-of-1036] (Section 6.15)

Header field name: Approved
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.1)

Header field name: Archive
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.2)

Murchison, et al. Standards Track [Page 26]

RFC 5536 Netnews Article Format November 2009

Header field name: Article-Names
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [Son-of-1036] (Section 6.17)

Header field name: Article-Updates
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [Son-of-1036] (Section 6.18)

Header field name: Comments
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2),
[RFC5322] (Section 3.6.5)

Header field name: Control
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.3)

Header field name: Date
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.1),
[RFC5322] (Section 3.6.1)

Header field name: Date-Received
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [RFC0850] (Section 2.2.4)

Header field name: Distribution
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.4)

Murchison, et al. Standards Track [Page 27]

RFC 5536 Netnews Article Format November 2009

Header field name: Expires
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.5)

Header field name: Followup-To
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.6)

Header field name: From
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.2),
[RFC5322] (Section 3.6.2)

Header field name: Injection-Date
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.7)

Header field name: Injection-Info
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.8)

Header field name: Keywords
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2),
[RFC5322] (Section 3.6.5)

Header field name: Lines
Applicable protocol: netnews
Status: deprecated
Author/change controller: IETF
Specification document(s): This document (Section 3.3.1)
Related information: [RFC3977] (Section 8.1)

Murchison, et al. Standards Track [Page 28]

RFC 5536 Netnews Article Format November 2009

Header field name: Message-ID
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.3)
Related information: [RFC5322] (Section 3.6.4)

Header field name: Newsgroups
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.4)

Header field name: NNTP-Posting-Date
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): none

Header field name: NNTP-Posting-Host
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [RFC2980] (Section 3.4.1)

Header field name: Organization
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.9)

Header field name: Path
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.5)

Header field name: Posting-Version
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [RFC0850] (Section 2.1.2)

Murchison, et al. Standards Track [Page 29]

RFC 5536 Netnews Article Format November 2009

Header field name: References
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.10),
[RFC5322] (Section 3.6.4)

Header field name: Relay-Version
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [RFC0850] (Section 2.1.1)

Header field name: Reply-To
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2),
[RFC5322] (Section 3.6.2)

Header field name: See-Also
Applicable protocol: netnews
Status: obsoleted
Author/change controller: IETF
Specification document(s): [Son-of-1036] (Section 6.16)

Header field name: Sender
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2),
[RFC5322] (Section 3.6.2)

Header field name: Subject
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.1.6),
[RFC5322] (Section 3.6.5)

Header field name: Summary
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.11)

Murchison, et al. Standards Track [Page 30]

RFC 5536 Netnews Article Format November 2009

Header field name: Supersedes
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.12)

Header field name: User-Agent
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.13)
Related information: [RFC2616] (Section 14.43)

Header field name: Xref
Applicable protocol: netnews
Status: standard
Author/change controller: IETF
Specification document(s): This document (Section 3.2.14)

7. References

7.1. Normative References

[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.

[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types",
RFC 2046, November 1996.

[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996.

[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Five: Conformance Criteria
and Examples", RFC 2049, November 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating
Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183,
August 1997.

Murchison, et al. Standards Track [Page 31]

RFC 5536 Netnews Article Format November 2009

[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
Encoded Word Extensions: Character Sets, Languages,
and Continuations", RFC 2231, November 1997.

[RFC3282] Alvestrand, H., "Content Language Headers", RFC 3282,
May 2002.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.

[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.

[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.

[RFC5537] Allbery, R., Ed. and C. Lindsey, "Netnews Architecture
and Protocols", RFC 5537, November 2009.

7.2. Informative References

[Errata] "RFC Editor Errata",
<http://www.rfc-editor.org/errata.php>.

[ISO3166-1] International Organization for Standardization, "ISO
3166-1:1997. Codes for the representation of names of
countries and their subdivisions -- Part 1: Country
codes", 1997.

[PGPVERIFY] Lawrence, D., "Authentication of Usenet Group Changes
(pgpverify)", June 1999,
<ftp://ftp.isc.org/pub/pgpcontrol/README.html>.

[RFC0822] Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.

[RFC0850] Horton, M., "Standard for interchange of USENET
messages", RFC 850, June 1983.

[RFC1036] Horton, M. and R. Adams, "Standard for interchange of
USENET messages", RFC 1036, December 1987.

[RFC2156] Kille, S., "MIXER (Mime Internet X.400 Enhanced
Relay): Mapping between X.400 and RFC 822/MIME",
RFC 2156, January 1998.

Murchison, et al. Standards Track [Page 32]

RFC 5536 Netnews Article Format November 2009

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee,
"Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616,
June 1999.

[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.

[RFC2980] Barber, S., "Common NNTP Extensions", RFC 2980,
October 2000.

[RFC3156] Elkins, M., Del Torto, D., Levien, R., and T.
Roessler, "MIME Security with OpenPGP", RFC 3156,
August 2001.

[RFC3696] Klensin, J., "Application Techniques for Checking and
Transformation of Names", RFC 3696, February 2004.

[RFC3851] Ramsdell, B., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message
Specification", RFC 3851, July 2004.

[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.

[RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)",
RFC 3977, October 2006.

[Son-of-1036] Spencer, H., "Son of 1036: News Article Format and
Transmission", Work in Progress, May 2009.

[USEAGE] Lindsey, C., "Usenet Best Practice", Work in Progress,
March 2005.

Murchison, et al. Standards Track [Page 33]

RFC 5536 Netnews Article Format November 2009

Appendix A. Acknowledgments

As this document is the result of an eight-year effort, the number of
people that have contributed to its content are too numerous to
mention individually. Many thanks go out to all past and present
members of the USEFOR Working Group of the Internet Engineering Task
Force (IETF) and its accompanying mailing list.

Appendix B. Differences from RFC 1036 and Its Derivatives

This appendix contains a list of changes that have been made in the
Netnews article format from earlier standards, specifically
[RFC1036].

o The [RFC5322] conventions for parenthesis-enclosed <comment>s in
header fields are supported in all newly defined header fields and
in header fields inherited from [RFC5322]. They are, however,
still disallowed for performance and/or compatibility reasons in
the Control, Distribution, Followup-To, Lines, Message-ID,
Newsgroups, Path, Supersedes, and Xref header fields.

o Multiple addresses are allowed in the From header field.

o [FWS] is permitted in Newsgroups header fields.

o An enhanced syntax for the Path header field enables the injection
point of, and the route taken by, an article to be determined with
more precision.

o Only one (1) message identifier is allowed in the Supersedes
header field.

o MIME is recognized as an integral part of Netnews.

o There is a new Injection-Date header field to make the rejection
of stale articles more precise and to minimize spurious
rejections.

o There are several new optional header fields defined, notably
Archive, Injection-Info, and User-Agent, leading to increased
functionality.

o Certain header fields, notably Lines, have been deprecated or made
obsolete (Section 3.3).

o The convention to interpret subjects starting with the word "cmsg"
as a control message was removed.

Murchison, et al. Standards Track [Page 34]

RFC 5536 Netnews Article Format November 2009

o There are numerous other small changes, clarifications, and
enhancements.

Appendix C. Differences from RFC 5322

This appendix lists the differences between the syntax allowed by the
Netnews article format (this document) as compared to the Internet
Message Format, as specified in [RFC5322].

The Netnews article format is a strict subset of the Internet Message
Format; all Netnews articles conform to the syntax of [RFC5322].

The following restrictions are important:

o A SP (space) is REQUIRED after the colon (':') following a header
field name.

o A slightly restricted syntax of <msg-id> (to be used by the
Message-ID, References, and Supersedes header fields) is defined.

o The length of a <msg-id> MUST NOT exceed 250 octets.

o Comments are not allowed in the Message-ID header field.

o The CFWS between <msg-id>s in the References header field is not
optional.

o It is legal for a parser to reject obsolete syntax, except that:

* The <obs-phrase> construct MUST be accepted.

* The obsolete <zone> "GMT" MUST be accepted within a
<date-time>.

o Every line of a header field body (including the first and any
that are subsequently folded) MUST contain at least one non-
whitespace character. This means that an empty header field body
is illegal.

Murchison, et al. Standards Track [Page 35]

RFC 5536 Netnews Article Format November 2009

Authors' Addresses

Kenneth Murchison (editor)
Carnegie Mellon University
5000 Forbes Avenue
Cyert Hall 285
Pittsburgh, PA 15213
U.S.A.

Phone: +1 412 268 2638
EMail: [email protected]

Charles H. Lindsey
University of Manchester
5 Clerewood Avenue
Heald Green
Cheadle
Cheshire SK8 3JU
U.K.

Phone: +44 161 436 6131
EMail: [email protected]

Dan Kohn
Healing Thresholds
211 N End Ave Apt 22E
New York, NY 10282
U.S.A.

Phone: +1 415 233 1000
EMail: [email protected]

Murchison, et al. Standards Track [Page 36]